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    <!-- 原始  刚接触js的时候  用的什么写什么 

        函数封装

        面向过程  


        面向对象  
            自定义对象;   { pop : function(), push : function() }



        数组对象:  var arr1 = [1,2,3] ; var arr2 = ["a","b","c"];

        arr1.pop()   arr2.push()
    -->
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